Cardiac catheterization is done using a thin, soft tube called a catheter. A doctor inserts the catheter into a blood vessel, often in the wrist, groin, or neck, using a special needle. The doctor then slowly guides the catheter through blood vessels toward the heart. The catheter may be moved into the left side or right side of the heart. The catheter tip is moved into various positions in the heart's chambers and vessels (coronary arteries).